Université de Paris 7, France.
Green functions for open shell
The calculation of Green functions for open shell
systems is combinatorially more complex than the
usual Green functions theory.
Hopf algebraic methods proved to be particularly convenient
to tame this complexity and provided perturbative and
For example, an algorithm will be given to calculate perturbatively
the generating function of the connected Green functions
and a nonperturbative hierarchy of Green functions will be
derived for open shell systems.